1. Field of the Invention
This invention relates to puffer type gas interrupters, and in particular concerns itself with puffer type gas interrupters which are suitable for handling large currents.
2. Description of the Prior Art
When an interrupter is required to carry a large current, at times of interruption when the contacts of the interrupter separate, the large current being passed causes an arc to form across the opened contacts. This arc, unless extinguished, can damage the contacts, causing pitting, and ultimately greatly shortening the life of the contacts. Thus to combat the problem of arcing, the puffer type gas interrupter was developed, wherein a gas puffer mechanism comprising, typically, a movable puffer cylinder running over a sliding puffer piston. The movable puffer cylinder contains an insulating gas which is compressed by the puffer mechanism which is operated at the time of interruption, and the gas is forcefully ejected through an aperture at the front of the puffer cylinder to blow out any arc that is formed.
Typically the puffer type gas interrupters of the prior art were constructed with the interrupter comprising an insulating housing filled with an arc extinguishing gas and containing a central tubular arc contact set consisting of a movable arc contact and a stationary arc contact over which the movable arc contact slides in electrical contact when the interrupter is closed. Around the movable arc contact and in sealing sliding contact therewith is a fixed, stationary puffer piston over which sealingly slides a puffer cylinder which is rigidly mechanically fixed to the movable arc contact to move therewith, and into one end of which the puffer piston slides and the other end of which is closed except for an aperture surrounding the central tubular movable arc contact at a certain distance to allow the insulating gas contained therein to be forced out when an interruption causes the movable arc contact to be drawn, pulling the puffer cylinder with it over the puffer piston. The gas thus forced out is guided by a funnel-like flow guide of an insulating material fixed to the front of the puffer cylinder, thus forming a gas flow to blow out any arc that forms. The current carrying capacity of the device is beyond that enabled by the arc contact set alone by using the body of the puffer cylinder to form a circuit between contacts, such as a cluster of finger-like contacts of a segmented slotted-finger construction, disposed on the movable arc contact side and the stationary arc contact side. The segmented slotted-finger contacts make sliding contact with the puffer cylinder permanently on the movable arc contact side, and at times of normal operation when the interrupter is closed, on the stationary arc contact side.
In recent year, however, the main circuit currents which interrupters have been required to handle have becoming increasingly large. The puffer type gas interrupters of the prior construction just discussed, in order to increase the current carrying capability, it is necessary to increase the current carrying cross-sectional area by enlarging the thickness or the diameter of the puffer cylinder. However, in increasing the thickness of the puffer cylinder, its effective conducting area (related to the depth of the surface skin) which is determined by the material employed, ceases to show improved effect beyond a certain increase in thickness. And in increasing the diameter, an adverse effect on the pressure rise characteristics of the compressed gas blown at the arc during interruption may occur, and the gas flow may alter, affecting interruption performance, and so necessitating a modification in the operation mechanism, which is the drive source.
Accordingly, in the prior art, when it was necessary to alter the current carrying capacity of the interrupter, it was also necessary to change the design of other structural elements such as the puffer piston, etc. Therefore it was extremely difficult to alter the current carrying capacity of existing interrupters, and in many instances, it was necessary to replace the entire interrupter. Also, it was difficult to meet future changes in current carrying capacity demands. Further, it was difficult for the manufacturer to produce a series of interrupters consisting of interrupters of various current carrying capacities.